1. Field of the Invention
The present invention relates to an ink jet print head having a plurality of nozzles which are arranged in a plurality of lines and from which ink can be ejected, an ink jet printing apparatus using the ink jet print head, and a method for manufacturing the ink jet print head.
2. Description of the Related Art
Printing apparatuses based on an ink jet system (ink jet printing apparatuses) have been applied to many printers, facsimile machines, copiers, and the like; the ink jet system causes ink to be ejected from nozzles arranged in an ink jet print head to print images on print media. In particular, color printers capable of printing color images using a plurality of color inks are commonly used owing to the improved quality of images obtained.
In addition to the improved quality of printed images, an increase in print speed is important to the ink jet printing apparatuses. Much effort has been made to increase the print speed by increasing the driving frequency with which ink is ejected from the print head as well as the number of nozzles arranged in the print head. A technique for sharply increasing the print speed involves, for example, increasing the length of the print head and the density at which the nozzles are arranged and printing an image by means of a single scan, which previously required a plurality of scans to complete.
As a method for increasing the length of the print head, arranging a plurality of print heads in a line is excellent for a reduction in manufacture costs. Specifically, if each print head is composed of chips comprising print elements (including nozzles), a long print head is constructed by arranging a number of chips corresponding to a plurality of original print heads. In the description below, the joining portion between the chips comprising the print elements corresponds to the joining portion between the print heads.
An image defect like a white stripe is likely to occur in that part of a printed image which corresponds to the joining portion between the print heads. This is because an air current generated between the print head and a print medium causes ink droplets ejected from an end of a nozzle line to impact the print medium at a position corresponding to the inside of the nozzle line instead of the correct position (this phenomenon is also referred to as an “end misdirection”).
To correct the deviation of the ink droplet impacting position caused by the end misdirection in a serial scan type ink jet printing apparatus, it is possible to gradually increase the pitch between nozzles located near the end of the nozzle line. Other possible causes of a stripe-like image defect include a difference in the amount of ink ejected among the nozzles, the accuracy with which the chips are arranged in a line, and a variation in the time when ink droplets impact the print medium.
As a technique for preventing a stripe-like image defect in that part of the printed image which corresponds to the joining portion between the print heads, a method of allowing the two sets of nozzles in the respective print heads to overlap each other in the joining portion has been proposed in, for example, Japanese Patent Application Laid-Open No. 5-57965.
The print heads with the overlapping nozzles suppress generation of a large white stripe. However, the ink droplet impacting position still deviates as a result of the end misdirection. A thin white stripe may thus appear in that part of the printed image which corresponds to the area in which the two sets of nozzles overlap. This stripe may be recognized as an image defect. This is particularly marked if glossy paper or the like which is suitable for printing high-quality images is used as the print medium.
If the pitch between the nozzles located near the end of the nozzle line is changed to correct the deviation of the ink droplet impacting position, an exposure mask or the like which is used in the process of producing nozzles must be changed. This sharply increases the manufacture costs of the print heads.